1. Field of the Invention
The present invention relates to a flat panel detector made up by use of thin film techniques and adapted for reception of radiation rays.
2. Description of the Related Art
Such a flat panel detector is constituted with circuits including the film transistors (hereafter called xe2x80x9cTFTxe2x80x9d) and other devices, the circuits being laminated by repeating such processes that a thin film is formed, e.g. on one side of a glass substrate, and patterned by an etching, then another thin film is formed thereon and additionally patterned.
FIG. 11 shows a conventional flat panel detector.
This flat panel detector has a constitution in which a plurality of pixels 30) are arrayed like a lattice on a plane, and is provided with signal lines 5 for reading signals of the pixels 30 outside, and vertical selection lines 6 for selecting pixels arrayed in crossing direction to the signal lines 5. Each pixel 30 includes a photoelectric conversion device 2 for generating a quantity of electric charges depending on an amount of incident light or a dose of incident X-rays, a capacitor 3 for accumulating generated charges, and a signal read-out TFT 4 for reading accumulated charges as a signal.
The photoelectric conversion device 2 may be a selenium device adapted for direct conversion from X-ray to electric charge, which may be substituted with the combination of a sensitized sheet and a photo diode.
With an on-voltage applied to an arbitrary vertical selection line 6, TFT 4 becomes conductive at a respective pixel 30 in a row connected to the vertical selection line 6, and accumulated charges in capacitor 3 of the pixel 30 flow through the TFT 4 to a signal line 5, to be read out at an external integration amplifier 7. After the read-out, an off-voltage is applied to the vertical selection line 6 and an on-voltage is applied to a subsequent vertical selection line 6 by a vertical shift register 8, and a signal is read out from a respective pixel 30 in a subsequent row. Such operations are repeated to read out one picture.
In the conventional flat panel X-ray detector, circuits ale substantially constituted by laminating thin films, with small inter-layer distances so that conductor lines in different layers have relatively large wiring capacities developed therebetween, in particular at cross regions between signal lines 5 and vertical selection lines 6, causing a signal-to-noise (hereafter referred to xe2x80x9cS/Nxe2x80x9d) ratio of a read picture co be decreased.
Further, signals in a column of pixels are read substantially by a single signal line, taking a corresponding interval of time for signal read-out.
Further, when increasing pixel integrity, the difficulty of proportional scale-down of TFT makes hard the provision of a sufficient pixel capacity.
Further, from a spatial restriction due to one-side installation, it is difficult to effect a desirable change of pixel capacity in accordance with photographing conditions.
Further, a necessary lime interval for reading one picture constitutes a minimum unit time to which associated operations are bound and in which no different actions are allowed for a single flat panel detector. For example, within a unit time in which a first picture is taken and its signal is held, it is unable for the detector to answer a desire for a second picture.
The present invention has been made with such points in view, and has it for the object to provide a radiographic flat panel detector permitting a decreased wiring capacity allowing an improved S/N ratio, a shorter signal read-out time, a higher pixel integrity with a secured pixel capacity, charge accumulation capacities to be switched in accordance with photographic conditions, an image holding condition allowing a picture to be photographed, or a photography at a different angle to cope with accompanied disturbances.
To achieve the object, an aspect of the invention provides a radiographic flat panel detector comprising a substrate, a first circuit formed on one side of the substrate and a second circuit formed on a different side of the substrate, the first and second circuits including a plurality of photoelectric conversion devices, a plurality of capacitors and a plurality of switching devices, and an electric contact provided through the substrate for interconnection between the first and second circuits.
According to this aspect, two circuits that are electrically and optically separated from each other by a thickness of a substrate and electrically interconnected by an electric contact are formed in regions on both front and back sides of the substrate, so that the integration density per unit area of substrate surface can be increased, in addition to that the two circuits can be allotted either as part of a radiation detecting circuit to be electrically or optically separated and the other as the rest, or can be constituted as a pair of radiation detecting circuits to be electrically or optically separated from each other.
Another aspect of the invention provides a radiographic flat panel detector in which a plurality of capacitors for accumulating electric charges generated by a plurality of photoelectric conversion devices receiving radiated rays are arrayed together with a plurality of switching devices in a matrix on a substrate, wherein the radiographic flat panel detector has xe2x80x9ca contact hole that makes electrical contact between front and back sides of the substrate by an electrically conductive substance buried in a minute through hole opened in the substratexe2x80x9d (hereafter sometimes simply referred to xe2x80x9celectric contact holexe2x80x9d or xe2x80x9ccontact holexe2x80x9d).
According to this aspect, by provision of a contact hole for electrical interconnection between front and back sides of a substrate, it is allowed for the front and back sides of the substrate to be each formed with a pixel made up of components such as a photoelectric conversion device, a capacitor and a switching device or part of pixel or associated components, as the components formed on the front and back sides of the substrate can be connected via the contact hole, to thereby constitute a flat panel detector making use of front and back sides of substrate, permitting an improved flexibility in component arrangement, when increasing pixel density.
For the provision of an electric contact between front and back sides of a substrate, one may employ the method of opening a minute hole through a photosensitive glass. The photosensitive glass comprises a silicate glass having metallic ions melted with an added sensitizing agent, which glass is photosensitive to ultraviolet rays, and has under heat processing a tendency to generate metallic colloids and crystallize, as they constitute cores. Resultant crystals are very fine and easily dissolves in acid, permitting a minute processing such as formation of a hole complicated in configuration. Such a minute hole may be stuffed with an electrically conductive substance to provide an electric contact between front and back sides of the glass.
Another aspect of the invention provides a radiographic flat panel detector in which a plurality of capacitors for accumulating electric charges generated by a plurality of photoelectric conversion devices receiving radiated rays are arrayed together with a plurality of switching devices in a matrix on a substrate, wherein the radiographic flat panel detector has contact holes that makes electrical contacts between front and back sides of the substrate by an electrically conductive substance buried in minute through holes opened in the substrate, numbers of capacitors for accumulating electric charges generated from a number of photoelectric conversion devices and numbers of switching devices are arranged in matrices on both of the front and back sides of the substrate, and the number of photoelectric conversion devices for receiving radiated rays to generate electric charges are provided simply on one side of the substrate, capacitors formed on the other side are adapted via the contact holes for accumulating electric charges generated from photoelectric conversion devices on the one side, and switching devices are provided on the both sides, respectively to independently switch for electric charges generated by the photoelectric conversion devices to be or not to be introduced to capacitors formed on the both sides.
According to this aspect, as photoelectric conversion devices are provided on a radiant ray reception side, switching devices are operable, e.g., for capacitors formed on a front side of a substrate to accumulate signals of a picture, and on or before read-out of signals from those capacitors, switching devices are operable for capacitors formed on a back side of the substrate to accumulate signals of another picture, thus permitting two pictures to be photographed without delay.